Turn lens on a famous Admiral (6)
I believe the answer is:
nelson
'a famous admiral' is the definition.
(I've seen this before)
'turn lens on' is the wordplay.
'turn' indicates anagramming the letters.
'lens' is an anagram of 'nels'.
'nels'+'on'='NELSON'
(Other definitions for nelson that I've seen before include "Naval hero who died at Trafalgar" , "One-eyed English admiral seen on pillar" , "Horatio or Mandela?" , "English admiral, lover of Lady Hamilton" , "English naval commander - wrestling hold" .)